For subsequent references to a source you have already cited, you may simply give the author's last name, a short form of the title, and the page or pages cited. A short form of the title of a book is italicized; a short form of the title of an article is put in quotation marks.

4. Mallard, One Fine Day, 13.

How to use Ibid.

When you have two notes from the same source, that follow each other consecutively,you may use "Ibid." (from the Latin, meaning "in the same place"), and the page number for the second and subsequent notes. Use "Ibid." alone if the page number is the same.